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Performance analysis of polyurethane insulation materials. Polyurethane rigid foam insulation materials used in construction represent an important segment of the polyurethane industry; they are characterized by their versatility, offering functions such as insulation and water resistance. These types of products have been in use in the European construction industry since the 1960s, meaning they are 40 years old now; in some places, legislation even designates polyurethane as the material to be used for insulation and waterproofing in construction. In recent years, with the rapid development of China’s building energy-saving market, polyurethane rigid foam insulation products have been widely used in building insulation and waterproofing applications, and have become one of the dominant energy-saving insulation products in this market. Polyurethane (i.e., polyamino carbonate, abbreviated as PU) is a polymer compound that contains many repeated —NHCOO— groups in its polymer backbone. Polyurethane products are generally high-molecular compounds obtained through polymerization reactions, using di- or polyorganic isocyanates and polyols along with various additives. When both of these main components contain two or fewer hydroxyl functional groups, the polymerization yields linearly structured compounds; whereas if one or both of the components have some or all functional groups consisting of three or more atoms, then polymers with a three-dimensional structure are formed. Due to these differences in structure, the properties of polyurethanes vary greatly. Just like steel, although they are all iron-carbon alloys, different ratios of iron to carbon and varying heat treatment processes result in vastly different properties. Polyurethane raw materials are widely used in various industries. Due to the characteristics of these industries and the products produced, different industries have varying requirements regarding the properties of composite materials that use polyurethane as their main component. Polyurethane rigid foam (SPF), which serves both insulation and waterproofing functions, is also completely different from polyurethane (PUR) used in refrigerators and cold storage for insulation purposes only. Although their external structures may appear very similar, as a material that combines insulation and waterproofing in building applications, polyurethane rigid foam overcomes the common problems associated with traditional building materials: the limitation of having only one function, the fact that waterproofing materials do not provide insulation, and the inverse situation where insulation materials fail to provide waterproofing. In addition, when there is a leak in the waterproofing layer, the insulation layer loses its insulating capabilities as well. Compared with other single-function insulation or waterproofing materials, rigid polyurethane foam has significant advantages: ¹. Rigid polyurethane foam can be used for multiple purposes, offering functions such as insulation, waterproofing, sound insulation, and vibration absorption ； ². It boasts excellent thermal insulation properties; it is the insulation material with the lowest thermal conductivity among all building materials available in China at present (≤0.024), thanks to its green, fluorine-free foaming technology, and it also has the highest thermal resistance value. Its thermal conductivity is only half that of EPS foam polystyrene boards ； ³. Rigid polyurethane foam features a continuous and dense surface layer, as well as nearly 100%% highly strong interconnected wall cells, resulting in ideal water impermeability. The spraying method is used for construction to achieve a continuous, seam-free waterproof and insulating layer, resulting in a seamless roof and an integrated external wall insulation enclosure with excellent waterproofing and impermeability properties ； 4. Excellent self-adhesive properties (no intermediate bonding materials required); it bonds firmly to rooftops and exterior walls, offering good resistance to wind uplift and negative wind pressure ； 5. Overall spraying construction to completely eliminate \"thermal joints\" and \"cold bridges\"” ； 6. Flexible gradient technology can effectively prevent cracking of the waterproof layer ； 7. Mechanized operations, automatic batching, consistent quality, fast construction with short cycle times ； 8. It has stable chemical properties, a long service life, and does not cause pollution to the surrounding environment ； 9. It extinguishes itself when away from an open flame; during combustion, it only carbonizes without dripping, and the size and shape of the carbonized layer remain essentially unchanged. This allows it to effectively prevent air from entering, thus stopping the spread of fire, giving it excellent fire safety properties. The quality of the properties inherent in polyurethane rigid foam materials has a significant impact on the safety of buildings, as well as on their insulation and waterproofing capabilities; therefore, it is essential to pay close attention to this aspect when selecting materials. The significant differences in performance between polyurethane rigid foam insulation materials used in the construction industry and those used for cold storage and refrigerators are mainly reflected in four performance indicators: elongation at break, closed-cell content, dimensional stability, and adhesion strength. One of the differences is elongation at break. Elongation at break is an important performance indicator that measures a polyurethane rigid foam’s ability to resist stress without undergoing permanent deformation; cold storage units and refrigerators that serve only for insulation purposes and do not have waterproof functions have no requirements regarding this key performance indicator. **The building materials industry standard (JC/Þ998-²006) specifies that when polyurethane rigid foam is used as an integrated material for waterproofing and insulation in roofs and walls, it must meet the requirement of an elongation rate of more than 10%% in order to prevent the waterproof layer from cracking, bulging, or splitting due to changes in ambient temperature, drying and swelling of roofs and walls, freeze-thaw damage in severe winters, as well as uneven settlement of building foundations. To enable polyurethane rigid foam to deliver excellent insulation properties while also showcasing its reliable waterproofing capabilities, only polyurethane rigid foam whose elongation rate meets the aforementioned **industry standards** can ensure that buildings remain warm in winter and cool in summer, providing a comfortable living environment; it also ensures that roofs do not leak and that exterior walls are free from moisture problems. The second difference: rate of dimensional change. Polyurethane rigid foam experiences certain changes in size and volume due to variations in the operating temperature. The magnitude of this rate of dimensional change is influenced by various factors such as the type of raw materials, the structure of the foam, the density of the core material, the molding process, and the type of blowing agent. Polyurethane rigid foam with good temperature resistance should not exhibit significant changes in size within an operating temperature range of -20 degrees Celsius to +80 degrees Celsius. Rigid polyurethane foam has a cell closure rate of over 95%%. The gas pressure trapped within the cells changes with variations in ambient temperature. If the structural strength of the foam walls is low, the foam will undergo deformation due to thermal contraction at low temperatures or expansion at high temperatures as a result of these changes in gas pressure within the cells. The greater the relative degree of dimensional change (i.e., the rate of size variation), the higher the likelihood that the polyurethane waterproofing and insulation layer will crack or develop openings. According to the **industry standard JC/Þ998-2006**, polyurethane rigid foam used in construction should have a dimension change rate of ≤1%, in order to accommodate the excessive contraction and expansion of the linear dimensions of exterior wall cladding systems caused by rapid changes in temperature differences between day and night during hot summers and severe winters. Dimensional stability is clearly closely related to the safe use of exterior wall cladding systems; the higher this value, the worse the safety performance. Polyurethane rigid foam with a dimensional change rate greater than 1% does not meet the requirements of **building materials industry standards**. Third difference: Closed-cell ratio. The closed-cell ratio is an important indicator for measuring a material’s water absorption rate and thermal conductivity. Materials with a low closed-cell ratio have higher water absorption rates and thermal conductivities, which has a crucial impact on their insulation properties as well as their resistance to freeze-thaw cycles. When polyurethane rigid foam is used as a waterproofing and insulating material for roofs, its foam’s closed-cell ratio should be at least 95%%. When this ratio is below 70%%, short periods of heavy rain do not cause leaks in the roof. However, during seasons with continuous rainy weather, as the rigid foam remains submerged in rainwater for extended periods, the open cells absorb more water. The rainwater that enters these cells will, under the force of gravity, seep through the connected cells into the roof’s underlying structure, where it gets trapped between that structure and the rigid foam. Even after the rain stops, it is difficult for this water to drain upward through the insulating and protective layers of the rigid foam under the influence of the intense sunlight. On the contrary, as the roof is exposed to sunlight, the upper layer becomes warm while the lower layer remains cool; as a result, moisture moves toward the lower layer of the roof. This leads to the abnormal phenomenon of no leaks on rainy days but leaks on sunny days, a problem that is particularly severe during the plum rain season in the south. Fourth difference: the impact of tensile strength and self-adhesion strength. The overall strength of polyurethane rigid foam exterior wall insulation systems depends on the tensile strength of the polyurethane material itself (which represents the weakest link in the system’s strength); therefore, the tensile strength of the polyurethane rigid foam is essentially the tensile strength of the entire exterior wall cladding system. For example: the tensile strength of rigid polyurethane foam is 200 kpâ, and the tensile pull strength of the entire exterior wall system is also 200 kpâ ； If this value drops to 100 kpâ, the tensile strength of the entire exterior wall system will be reduced to half of its original value, and the safety factor will also drop sharply to half of its original level. Furthermore, when formulating spray polyurethane rigid foam for use in the construction industry, it is necessary to fully consider the adhesive strength requirements associated with external wall insulation systems; therefore, such foam is required to have excellent self-adhesive properties with building materials such as metal, concrete, masonry, wood, and glass. **Both the building materials industry standard JC/Þ998-2006 and the recently adopted \"Technical Guidelines for External Insulation Systems Using Rigid Polyurethane Foam\", set mandatory requirements regarding the self-adhesion strength of rigid polyurethane foam. This is also an important indicator that underscores the clear safety advantages of spray-applied rigid polyurethane foam over external insulation systems using expanded polystyrene (EPS) and extruded polystyrene (XPS). It is worth noting that strength is the most important mechanical property of rigid polyurethane foam; its value directly determines the wind pressure resistance, impact resistance, strain resistance, and capacity to bear total weight of exterior wall cladding systems. It is the most important and direct performance indicator for assessing the safety of exterior wall insulation systems. In summary, when using rigid polyurethane foam as a dual-function material for building insulation and waterproofing, users must conduct strict evaluations of the material’s density, strength, elongation at break, dimensional stability, and closed-cell content in accordance with the requirements of the construction materials industry standard JC/Þ998-²006. As the only current new type of building material that combines insulation and waterproofing properties, rigid polyurethane foam insulation materials are still in their initial stage of application in China’s construction industry. Fortunately, in order to accelerate the innovation of building insulation materials and promote the use of rigid polyurethane foam in the field of building energy conservation, the Ministry of Construction established a dedicated \"Working Group for the Promotion of the Use of Polyurethane in Building Energy Conservation.\" Thanks to the high level of attention and strong support from the Ministry, significant progress has been made in the use of rigid polyurethane foam-based insulation and waterproofing materials in China’s building energy conservation industry.